Typically, with special respect to communication applications, a linear behavior of the employed components, especially of amplifiers, is not only desired but even necessary in order to ensure the avoidance of nonlinear distortion, and thus the prevention of an undesirable interference spectrum. In this context, due to the fact that in practice, there are no ideal components having a completely linear characteristic available, the performance of distorting components has to be optimized especially regarding linearity.
WO 99/05784 A1 discloses a correcting device for automatically correcting a high frequency power amplifier with the aid of predistortion. The correcting device has a mechanism for generating a reference carrier from a measured input signal of the high frequency power amplifier, and a synchronous demodulator for generating an input envelope curve from a reference signal. Nevertheless, the aforementioned document does not consider providing the reference signal not only for the purpose of generating a desired signal but also for the purpose of predistortion. As a consequence of the lack of providing the reference signal also for predistortion, the total noise is the sum of the noise floor of the system and the respective noise components of each of the elements involved in predistortion, which leads to a non-optimal, respectively faulty, predistortion, and thus to a not perfectly optimized performance of the amplifier with special respect to linearity. Another non-linear method of compensation is known from US 2016/0191020 A1.
The European patent application EP 16 192 718.1, which is incorporated by reference herein, shows a predistortion system and method, which allow for a significantly higher performance of the predistortion. The system and method shown there though are not optimal for some applications, since it is not possible to judge if the predistortion determined iteratively is suitable for a different waveform. Also, it is not possible to assure that the resulting predistortion filtering meets bandwidth conditions. Moreover, it is difficult to foresee the performance of the predistortion device trained with baseline signals, when using real-world signals.
Accordingly, there is a need to provide a predistortion system and a predistortion method for optimizing the performance of distorting components, which especially assure meeting bandwidth requirements and which function reliably with real-world signals.